I'm trying to play Riven: The Sequel to Myst with ScummVM (a nightly build admittedly) and while the transitions are still missing and the video is a bit muddier and less integrated than what it used to be, the thing that bothers me the most is that while it displays a proper resolution when it launches (windowed), I'd like to play it (and other SCUMMVM games) in a mode where it's full screen but a non-stretched, non-scaled mode. Yeah, I know it's going to be a lot of wasted screen real estate, but is there a mode for this at all?

Also you might need to check the settings of your screen and graphics card to make sure neither does scaling and/or stretching and that they instead do letter boxing when an application request a resolution smaller than what they support.